An FA (Factory Automation) system includes control target apparatuses and a control apparatus such as a programmable controller that performs predetermined arithmetic processing using states of the control target apparatuses as input data and outputs operation conditions of the control target apparatuses as output data. Communication means are provided in the control apparatus and the control target apparatuses to connect the control apparatus and the control target apparatuses via a network to thereby enable real-time control. Specifically, the communication means provided in the control target apparatuses are caused to function as slave stations. The communication means provided in the control apparatus is caused to function as a communication management station that controls data transmission of the slave stations. The communication management station receives data from the slave stations and periodically performs processing for transmitting data for controlling the control target apparatuses, which is computed by the control apparatus using the received data, to the slave stations. At this point, the communication management station controls timing of the data transmission by the slave stations to ensure real-time properties of data communication.
A data communication method employing a token passing system to ensure the real-time properties of the data communication is known. The token passing system is a system for feeding, in order, a token frame to communication nodes including a communication management station and slave stations present in a system and giving a transmission right to the communication nodes, whereby the communication nodes transmit data. It is possible to perform cyclic data communication by circulating the token frame at a predetermined period (see, for example, Patent Literature 1).
In Patent Literature 1, when a slave station cannot normally receive a data frame transmitted from the communication management station, the slave station transmits a data frame to the communication management station with information indicating abnormality included in a reception error occurrence detection field provided in the data frame. The communication management station retransmits the data frame, transmitted last time, to the transmission source of the data frame having the reception error occurrence detection field indicating abnormality.